Financial Instruments - Financing Receivables Continues to Accrue Finance Income (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	$ 10,029		$ 9,072
Related Unbilled Recorded Investment	112,381		119,354
Related Allowances	(1,070)		(994)
Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	460		323
Related Unbilled Recorded Investment	11,191		9,274
Related Allowances	(155)	$ (155)	(155)	$ (155)	$ (155)	$ (155)
Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	9,569		8,749
Related Unbilled Recorded Investment	101,190		110,080
Related Allowances	(915)	$ (839)	(839)	$ (839)	$ (839)	$ (922)
Financing Receivables Accrued and Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	1,980		1,494
Financing Receivables Accrued and Current | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	99		52
Financing Receivables Accrued and Current | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	1,881		1,442
Financing Receivables 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	2,163		2,084
Financing Receivables 30 to 89 Days Past Due [Member] | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	46		18
Financing Receivables 30 to 89 Days Past Due [Member] | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	2,117		2,066
Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	5,886		5,494
Financing Receivables Equal To Greater Than 90 Days Past Due [Member] | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	315		253
Financing Receivables Equal To Greater Than 90 Days Past Due [Member] | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	5,571		5,241
Financing Receivables Continue To Accrue Finance Income [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	7,773		8,173
Related Unbilled Recorded Investment	34,118		33,030
Related Allowances	0		0
Recorded Investment Net of Allowances	41,891		41,203
Financing Receivables Continue To Accrue Finance Income [Member] | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	389		283
Related Unbilled Recorded Investment	1,372		1,523
Related Allowances	0		0
Recorded Investment Net of Allowances	1,761		1,806
Financing Receivables Continue To Accrue Finance Income [Member] | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	7,384		7,890
Related Unbilled Recorded Investment	32,746		31,507
Related Allowances	0		0
Recorded Investment Net of Allowances	40,130		39,397
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables Accrued and Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	707		586
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables Accrued and Current | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	51		28
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables Accrued and Current | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	656		558
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	1,218		1,481
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables 30 to 89 Days Past Due [Member] | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	23		9
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables 30 to 89 Days Past Due [Member] | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	1,195		1,472
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	5,848		6,106
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member] | Net Investment in Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	315		246
Financing Receivables Continue To Accrue Finance Income [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member] | Net Financed Sales Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Billed Financing Receivables	$ 5,533		$ 5,860